UC Irvine

When the phenomena of smog and acid deposition were first recognized, it was largely gas phase chemists and photochemists who leapt into the fray to untangle the sources and chemistry involved. Over time, the importance of multiphase chemistry was recognized, as illustrated in a dramatic manner with the discovery of the Antarctic ozone hole which is driven by heterogeneous chemistry on polar stratospheric clouds. Since then, it has become clear that multiphase chemistry is central to both the lower and upper atmosphere and that this deeply intertwines interactions between the gas and condensed phases in the atmosphere. As a result, it can be argued that multiphase atmospheric chemistry begins … and ends… with gases. This paper is based on the 2018 Polanyi Medal award presentation at the 25th International Symposium on Gas Kinetics & Related Phenomena and traces research carried out in the author's laboratory on multiphase chemistry over a number of decades. While a great deal has been learned about these processes, they remain one of the areas of greatest uncertainty in understanding atmospheric composition, air quality, chemistry, and climate change.